Transition Device for Textured Protein Foodstuff

ABSTRACT

A device for transferring molten proteinaceous extrudate material from the exit of an extrusion cooker barrel to a cooling die whilst promoting or maintaining laminar flow of said molten extrudate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims the benefitand priority to U.S. patent application Ser. No. 17/044,660, filed Oct.1, 2020, which is a national stage application under 35 U.S.C. 371 ofPCT Application No. PCT/AU2019/050294 having an international filingdate of Apr. 4, 2019, which designated the United States, which claimsthe benefit of Australian Application Serial No. 2018901110, filed Apr.4, 2018. The entire specifications and figures of the above-referencedapplications are hereby incorporated in their entireties by reference.

TECHNICAL FIELD

The invention relates to the field of commercial extruded foodmanufacture. In particular, the invention relates to a device forshredding an extruded high moisture texturised protein food product.

BACKGROUND OF THE INVENTION

By 2050 the world's population is projected to reach 9 billion and ithas been suggested that 70% more food will be required to sustain thispopulation. Between 1950 and 2000 meat production increased from 45 to229 million tons and this is expected to further increase to 465 milliontons by 2050.

The relatively inefficient conversion of plant protein into animalprotein via animal metabolism makes meat production responsible for adisproportionate share of environmental pressures such as land use,freshwater depletion, global warming and biodiversity loss.

A solution to reduce the impact of meat production on the environment isoffered by partial replacement of meat protein with plant proteinproducts in the human diet. However, there is a desire that theseprotein products have favourable organoleptic properties, such asflavour and texture, when compared with meat.

Both the food industry and food scientists have been interested increating fibrous food textures for several decades now. High MoistureExtrusion Cooking (HMEC) technology as a concept has been establishedsince the early 1980's. It is a technology for texturising protein-richmaterials having a moisture content of greater than about 30% by mass.

In a typical HMEC process according to the prior art, the raw materialsare heated under pressure in an extrusion cooker until molten; theresulting melt is cooled and solidified in-situ by a cooling die toproduce aligned protein fibres from the melt, giving a product with afibrous internal texture that satisfies organoleptic requirements.

However, for the product to fulfil its purpose of accurately resemblingcooked muscle meat to the consumer, it is required that laminar flow ofthe molten extrudate is established prior to cooling and solidificationextrudate. However, designing equipment to achieve this condition hashitherto been characterised by trial-and-error. This also limits theability of the process to be successfully scaled up or adapted todifferent extrusion cooker and cooling die designs.

Accordingly, it is an object of the invention to provide a device a forestablishing laminar flow for HMEC extrudate exiting an extrusion cookerwhile transferring the extrudate to a cooling die that ameliorates atleast some of the problems associated with the prior art.

SUMMARY OF THE INVENTION

The invention is characterised by a device connecting the outlet of anextrusion cooker with the inlet of a cooling die, having an internalextrudate channel whose geometry is designed to induce laminar flow inthe molten extrudate exiting the extrusion cooker before it reaches thecooling die. In particular, the invention is characterised by therelationship between rheological characteristics of the extrudate andkey dimensions of the channel.

According to a first aspect, the invention provides a device fortransferring molten proteinaceous extrudate material from the exit of anextrusion cooker barrel to a cooling die whilst promoting or maintaininglaminar flow of said molten extrudate; wherein said device includes atransfer channel, through which extrudate flows immediately upon exitingthe extrusion cooker barrel; and wherein said transfer channelincorporates a transition zone, immediately adjacent the exit of theextrusion cooker barrel, that has an internal profile that transitionsfrom a shape matching the extrusion cooker barrel exit profile to acircular profile of diameter ‘d’, and a laminar flow development zonethat has said circular profile; and wherein said laminar flowdevelopment zone has a minimum length (L_(e)) equal to 0.006×d×Re, whered=transfer channel diameter and Re=the Reynolds number associated withthe flow of molten extrudate in said laminar flow development zone.

The device should also have an internal channel configuration whereinthe internal profile of said laminar flow development zone aconstriction zone wherein the internal diameter of the converges to asmaller diameter and then diverges to the diameter ‘d’.

The Reynolds number is a dimensionless number defined with respect to afluid flowing in an enclosed channel of diameter ‘d’ as follows:

Re=(ρ·v·L)/μ

Where:

v=mean velocity of the fluid (m/s);

L=hydraulic diameter (m) i.e. the diameter of the channel if circular,otherwise the ratio of four times the cross-sectional area to the wettedperimeter of the channel;

ρ=fluid density (kg/m³);

μ=dynamic viscosity (Pa·s).

The device as defined above will induce laminar flow in the moltenextrudate prior to the entry of the cooling die, as desired. The furtheradvantage of defining the cooling die in this way is that the design canbe successfully scaled up (or down) to higher (or lower) flow rateswhile still achieving laminar flow in the cooling die, which producesthe most desirable results regarding the internal texture of the cooledextrudate.

Preferably, the device further includes a transformation zone whereinthe channel has an internal profile that transitions from the circularprofile of the laminar flow development zone to a profile that matchesthe internal profile of said cooling die.

The constriction provides a bridge between the melt flow through thecross-sectional ‘FIG. 8 ’ aperture at the exit of the twin-screwextruder and the cooling die channel. It tends to stabilise the meltflow pattern from being partly rotational and turbulent at the exit ofthe extruder, towards stable, linear flow in the cooling die.

The linear velocity at the constriction is preferred to be at least 10%greater than the linear velocity exiting the extruder. Subsequently, thelinear velocity in the cooling die channel is preferred to be up to 10%greater than the linear velocity at the constriction. This velocitysequence dampens flow disruption and enhances fibre formation in thecooling die.

According to another aspect of the invention, there is provided a methodof designing a device for transferring molten proteinaceous extrudatematerial from the exit of an extrusion cooker barrel to a cooling diewhilst promoting or maintaining laminar flow of said molten extrudate;said device having an internal channel through which said extrudateflows comprising a laminar flow development zone and having a lengthL_(e); said method including:

Selecting an internal channel diameter (d);

Determining the average flow velocity (v) of the extrudate in saiddiameter;

Determining the density (ρ) of the extrudate;

Determining the viscosity (μ) of the extrudate;

Determining the hydraulic diameter (L) of the extrudate flowing in saidchannel;

Determining the Reynolds Number (Re) for the extrudate flow in saidchannel;

Calculating the length L_(e) by applying the formula: L_(e)=0.006×d×Re.

Now will be described, by way of a specific, non-limiting example, apreferred embodiment of the invention with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of device according to the invention shownconnected in between an extrusion cooker and a cooling die.

FIG. 2 is a schematic diagram illustrating types of fluid flow in achannel.

FIG. 3 is a schematic diagram illustrating the development of laminarflow of a fluid in a channel.

FIG. 4 is a cross-sectional drawing of a first part of a deviceaccording to the invention.

FIG. 5 is a schematic diagram of the profile of the extrudate flowchannel in a device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention may be embodied as a transfer device that is affixedbetween the exit end of an extrusion cooker and the inlet to a coolingdie, the device (which may be made of one or more parts) having aninternal channel through which molten extrudate flows, wherein thechannel has an internal geometry chosen to induce laminar flow of theextrudate at or before the point the extrudate enters the cooling die.

Part of the invention is the determination of the minimum requiredlength of this channel to achieve laminar flow at the cooling die. Thelonger the transition, the more likely the melt will achieve laminarflow. However, longer channels bring risks, such as that the melt maycool and partially coagulate, leading to caking, poor internal textureformation. Longer channels are also likely to be costlier and heavier,meaning they are less practical to use.

To explain the context of the invention, the process in which the deviceoperates is one that involves the transformation of blends of vegetableand animal proteins through an integrated cooking and cooling processthat produces a fibrous texture, representing a homogeneous mixture ofmeat and plant protein. Particularly, it provides a method for taking anuntextured, paste-like, batter-like protein product with no visiblegrain or texture and converting it into a texturised, fibrous proteinproduct having the consistency of cooked muscle meat.

The core transformational step in the process is the extrusion cooker(or ‘extruder’). The raw materials are heated in the main extruderbarrel until molten. The resulting melt cooled via a continuousthroughput cooling die after exiting the extruder to produce fibres fromthe melt, resulting in a product with a fibrous, chewy texture,characteristic of meat.

The cooling die is effectively a heat exchanger that enables aprogressive rate of solidification of the melt, which in turn generatesa laminated fibrous structure. The cooling die itself is a tubular steelconduit that defines the channel through which the product progresses,surrounded by a liquid-cooled jacket that progressively removes heatfrom the product, beginning as a molten liquid and exiting the coolingdie as a solid product with an internal ‘fibrous’ texture.

It is highly desirable that the flow of molten extrudate in the coolingdie is laminar in nature, as this produces the most desirable alignmentof the proteins and therefore the most desirable internal texture uponcooling.

In fluid dynamics, ‘laminar flow’ occurs when a fluid flows in parallellayers, with no disruption between the layers. At low velocities, thefluid tends to flow without lateral mixing, and adjacent layers slidepast one another: there are no cross-currents perpendicular to thedirection of flow, nor eddies or swirls of fluids, as per FIG. 2 .

Extrudate in an extrusion cooker barrel undergoes very turbulentconditions. Therefore, prior to entering a cooling die, the extrudatemust undergo some conditioning to achieve laminar flow. The inventorshave determined that this can be achieved by using a transition flowconditioning device, interposed between the extruder and the coolingdie, that has an internal geometry that will impose a laminar flowcondition on the extrudate, as illustrated in FIG. 3 .

In fluid dynamics, the Reynolds Number (Re) is a dimensionless numberthat can be used to express the flow characteristics of a fluid. It isthe ratio of the inertial force to the shearing force of the fluid: howfast the fluid is moving relative to how viscous it is, irrespective ofthe scale of the fluid system. It is defined as follows:

Re=(ρ·v·L)/μ

Where:

v=mean velocity of the fluid (m/s);

L=hydraulic diameter (m) i.e. the diameter of the channel if circular,otherwise the ratio of four times the cross-sectional area to the wettedperimeter of the channel;

ρ=fluid density (kg/m3);

μ=dynamic viscosity (Pa·s).

Typically, laminar flow occurs when the Reynolds number is below acritical value of approximately 2,040, though the transition range istypically between 1,800 and 2,100.

The inventors have determined that laminar flow can be induced into themolten extrudate by providing a transition channel that is circular inprofile. Therefore, it is necessary to transform the flow profile fromthe shape of the extruder outlet to a circular cylinder, to establishlaminar flow, and then (smoothly) to a shape matching the input and flowchannel profile of the cooling die.

The inventors have further determined that, for the type of fluidsnormally encountered in extrusion cooking of HMEC, a key aspect of thegeometry of a transition device is the length (L_(e)) of the cylindricalchannel post-transformation in profile from the extruder exit shape. Toestablish and maintain laminar flow, this length can be calculated as:

${\frac{L_{c}}{d} \approx {0.06{Re}_{d}}},{{f{or}}a{Laminar}{Flow}}$

Typically for these types of extrudates, the following conditions apply(for calculating Re):

v=0.5 to 3.5 m/min;

L=60 to 150 mm;

ρ=1048 kg/m³;

μ=50 to 500 Pa·s.

A major advantage of using a design parameter based on dimensionlessanalysis via the Reynolds number is that scale-up (or scale-down) of thesystem is much simpler, as the relationship will hold for alldimensions.

This calculation is applicable to the length of the transition channeloverall or can be applied to sub-sections of the transition channel.

It is also important to consider the angle at which the channelconstricts after the extruder exit. It is preferably not too rapid aconstriction, nor too slow a constriction, in the direction of flow.

Example—The feed materials are prepared according to their kind. If theformulation requires, meat is supplied in frozen blocks (approx. −18°C.) that are stripped and ground though a 13 mm hole plate andtransferred to a mixing grinder with a 5 mm hole plate. Here it iscombined with a first portion of water and a premixed blend of soyprotein, gluten and flavourings/seasonings and ground at approximately10° C. This mixture is transferred to an open throat progressing cavityof the extrusion cooker.

A second blend of soy protein, gluten and flavourings/seasonings is alsoprepared in a ribbon blender and transferred via a vacuum conveyer to aloss-in-weight feeder that meters the blend into a second feed-port inthe extrusion cooker, in parallel with a second portion of water.

The extrusion cooker in this example is a twin-screw co-rotatingextruder with a heated barrel, as supplied by Clextral, model BC72. Theextrusion cooker screw profile is designed for optimised performance fortexturization, based on increasing the residence time along the sectionsand enhancing specific mechanical energy input. In this embodiment, thescrew profile comprises, from feed to discharge: 42% conveying elements,42% CSTR (continuous stirred tank reactor) based mixing elements, and16% high pressure pumping elements.

The molten mixture then exits the extrusion cooker barrel via anaperture resembling a ‘figure-8’ shape and passes through the transitiondevice according to the invention into the cooling die.

The cooling die is typically a cross-flow heat exchanger, having ahollow stainless-steel conduit through which the product flows as it iscooled, and a surrounding jacket through which water is pumped to as acoolant to remove heat from the product. The conduit channel profile isrectangular in profile—145 mm wide and 20 mm deep.

As shown in FIG. 1 , the transition device is made up of two distinctpieces—a first ‘8 to O’ segment 5 that is affixed to the extrusioncooker 10, and an ‘O to die’ segment 15 than is affixed to the ‘8 to O’and to the cooling die 20.

The detail of the piece embodying the ‘8 to O’ segment is shown in FIG.4 . The ‘figure 8’ aperture 25 on the inlet matches the outlet apertureof the extruder barrel. There is a transition zone 30 that transformsthe ‘figure 8’ shape into a cylindrical profile 35 having a diameter of98.4 mm.

The laminar flow transition zone 40 begins at this point 45 in thispiece. The length of this zone is approximately 144 mm in length in thispiece.

The purpose of this piece is to dampen any ‘swirl’ generated by theco-rotating intermeshing screws of the extruder; maintain pressure ofthe flow; increase shear rate in the extrudate to accelerate flow togenerate non-disruptive linear flow; and to discourage flow separation,which would otherwise lead to short fibre formation, by utilising smoothinternal surfaces.

Preferably, the transition zone is internally heated, so that the melttemperature at the exit of the extruder is maintained to the coolingdie.

The piece 50 embodying the remainder of the laminar flow transition zoneand the transformation zone from cylindrical profile to the cooling diechannel profile is shown in FIG. 5 . It has an overall thickness of 103mm, and its internal channel profile 55 changes from circular profile of98.4 mm to a slit 145 mm wide and 20 mm deep throughout this length.

The two above described pieces are typically bolted together. Theinternal channel surfaces of both pieces should conform to the followingmaterial requirements: stainless steel 304 or similar (17-4PH, Stavax,Mirrax, 1.2316); good corrosion resistance properties, toughness, heatresistance and wear-resistant properties; uniform hardness in alldimensions; ease of machinability and high surface finish and polish.The preferred hardness is HRC 33-36 (Hardness Rockwell C). Internalsurface corners to be based on R20 curvature for smoothing. The surfacefinish to be at least equivalent to a 320 Grit Polished Surface andElectropolished to smooth out peaks yielding an Ra of 0.06μ.

It will be appreciated by those skilled in the art that the abovedescribed embodiment is merely one example of how the inventive conceptcan be implemented. It will be understood that other embodiments may beconceived that, while differing in their detail, nevertheless fallwithin the same inventive concept and represent the same invention.

1. A method of designing a device for transferring molten proteinaceousextrudate material from the exit of an extrusion cooker barrel to acooling die whilst promoting or maintaining laminar flow of said moltenextrudate; said device having an internal channel through which saidextrudate flows comprising a laminar flow development zone and having alength Le; said method including: Selecting an internal channel diameter(d); Determining the average flow velocity (v) of the extrudate in saiddiameter; Determining the density (p) of the extrudate; Determining theviscosity (μ) of the extrudate; Determining the hydraulic diameter (L)of the extrudate flowing in said channel; Determining the ReynoldsNumber (Re) for the extrudate flow in said channel; Calculating thelength Le by applying the formula: Le=0.006×d×Re.
 2. A method ofdesigning a device for transferring molten proteinaceous extrudatematerial from the exit of an extrusion cooker barrel to a cooling diewhilst promoting laminar flow of said molten extrudate; said devicehaving an internal channel through which said extrudate flows comprisinga first laminar flow development zone having a minimum length Le; and asubsequent cylindrical laminar flow zone; said method including:Selecting an internal channel diameter of the cylindrical laminar flowzone with reference to the geometry of the cooling die (d) in metres;Determining the average flow velocity (v) of the extrudate in saiddiameter in m/s; Determining the fluid density (ρ) of the extrudate inkg/m³; Determining the dynamic viscosity (μ) of the extrudate in Pa·s;Determining the hydraulic diameter (L) of the extrudate flowing in saidchannel; where the hydraulic diameter is the equivalent diameter of saidchannel if it were circular, otherwise the ratio of four times thecross-sectional area of the channel to the wetted perimeter of saidchannel; Determining the Reynolds Number (Re) for the extrudate flow insaid channel where Re=(ρ·v·L)/μ; Calculating the minimum length Le ofsaid first laminar flow development zone by applying the formula:Le=0.06×d×Re; Designing said device to have a laminar flow developmentzone having a flow length substantially equal to the calculated minimumlength Le; Fabricating a transition device having a laminar flowdevelopment zone having a flow length substantially as calculated in theprevious step; and Installing said transition device between saidextrusion cooker barrel and said cooling die.